Mars W cloud: Evidence of nighttime ice depositions

Abstract

Water clouds on Mars, their current and past connections with other forms of water, along with surface features that suggest the early existence of flowing water, continue to be intriguing aspects of the red planet. Discrete afternoon mountain clouds were one of the earliest atmospheric features to be observed on Mars. Their exclusive formation near the high mountains led to the common belief that air lifting associated with local circulation induced by the mountains underlies their formation. We demonstrate that an additional local source of water vapor is needed for the formation of opaque discrete afternoon clouds on the mountains of Mars, including the so-called W-formation. We suggest that the possible deposition of ice from the thick aphelion cloud belt during the night is capable of providing this additional source. This direct cloud water deposition on mountains on Mars bears many similarities with the well-known interception of water by mountains frequently immersed in fogs on Earth. Copyright 2009 by the American Geophysical Union.